There were hints before though of Sakura having some kind of feelings towards Naruto as well. I doesn't come right out, but the prospect of her actually LOVING Naruto wasn't so far-fetched at that point.

http://www.onemanga.com/Naruto/297/11/

Badass chapter though! This is the Naruto that we were used to before! I think the problem was that Kishi (or his intern, hahaha) didn't find a way to put the fighting potential spotlight on other characters without making Naruto look useless. Granted, Naruto hadn't shown an inability to fight really, but an inability to control his emotions in front of some of his prior conflicts.

In the end, Yamato was right when he said "you're about to see a completely new Naruto" when he was up against Kakuzu.